Doesn't work in IE11

Not sure what you're targeting as far as browser support but the following line blows up in IE11:  https://github.com/misund/hex-to-rgba/blob/6987950f59aeb765fcd1d39906a84fec0a2bb0fd/src/index.js#L1

This is because `String.prototype.startsWith` isn't supported as shown in this table: http://kangax.github.io/compat-table/es6/#test-String.prototype.startsWith